JPS61158068A - Optical disc reproducing device - Google Patents

Abstract

PURPOSE:To make the amplitude level of an RF signal constant by increasing the output of a current source when a peak value of the RF signal is higher than a reference voltage. CONSTITUTION:When the peak value Vp of the RF signal is higher than an RF signal reference voltage V2, an output V29 of a comparator circuit 29 controls an output of a current soruce 12 to be increased. As a result, a reference voltage V0 of an error voltage detection circuit 272 is decreased as VMD>V0, then a difference voltage decreases the output of a current source 13 of a PWM signal generating circuit 273. Thus, the slope of a sawtooth voltage signal Vramp fed to a comparator CMP1 is decreased, an L level pulse width of the comparator output is narrowered and the on-period of a switching transistor Q1 of an LD drive circuit 274 is shortened. Thus, the laser output of a laser diode LD is decreased and the amplitude (peak value) of the RF signal is decreased.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention is applicable to, for example, CDs (compact discs), VDs (
Regarding optical disc playback devices that play back optical discs such as video discs), RF
This invention relates to controlling laser output so that the double signal amplitude is constant.

[Technical background of the invention and its problems] Conventionally, for example, a CD type optical disc playback device (
A CD playback device (hereinafter referred to as a CD playback device) uses an optical pickup that irradiates one side of a disc with laser light and receives reflected light that changes depending on the presence or absence of bits formed on the disc surface. When a multi-segment type photodetector is used for the photodetector that receives the reflected light of this optical pickup, an RF signal as shown in FIG. 4 is used.
RF that corresponds to the presence or absence of the above bits using a signal amplification circuit
Taking out the signal.

That is, the reference numeral 11 in FIG. 4 is a four-part photodetector in the optical pickup, and each light-receiving area h! of this detector 11 is divided into four parts. ! After the signals extracted by photoelectric conversion in A and C of A-D are added with current, the first current voltage (1-V
) is converted into a first voltage signal -vl by the conversion circuit 12a,
The signals taken out by photoelectric conversion at B and D are similarly added with current, and then converted into a second voltage signal -2 by the second IV conversion circuit 12b. These voltage signals −Vl, −
Although not shown here, V2 is subtracted and taken out as a focus error signal, and is also connected to resistors R1 to R1, respectively.
The signals are added by an adder circuit 13 consisting of R3 and an operational amplifier A1 and taken out as an RF signal Vout corresponding to the presence or absence of a bit. Here, the power supply voltage supplied to the adder circuit 13 is set to Vcc, base IE'! If the pressure is V ref, the above RF signal Vout can be expressed as follows. The output waveform becomes as shown in FIG. 6(a), and reaches its maximum value at the total reflection level.

Incidentally, since the current outputted from each of the light receiving IN areas A to 0 of the detector 11 is only in one direction (the direction indicated by the arrow in the figure), the output voltage of each t-V conversion circuit 12a, 12b is -V.
l, -V2 swings only below the reference voltage Vref, and the output voltage yout of the adder circuit 13 swings only above the reference voltage Vrer.

By the way, the RF signal amplification circuit of the conventional optical disc playback device as described above does not have any problems when the power supply voltage Vcc is high, but when lowering the voltage for application to a portable type playback device, there is no problem. The following problems occur.

(1) If the electric tm voltage Vcc is lowered as it is, the RF signal vout will clip as shown in FIG. 6(b). To prevent this clipping, the gain must be lowered.

(2) If the gain is lowered as in (11), the next stage data slicing circuit (EFM signal generation circuit) cannot perform slice processing properly.

In order to solve the above problems, an RF signal amplification circuit as shown in FIG. 5 has been considered. That is, in this RF signal amplification circuit, the inverting input 1ti(-) of the operational amplifier A of the adder circuit 13 is connected to the VCC power supply via the level shift current source IO, and variable resistors VR, , , are connected in place of the resistor R3. 1 (hereinafter, this adder circuit will be referred to as a level shift adder circuit). In other words, the above problem is solved by supplying a current (O) from the current 110 to the inverting input terminal (-) of the operational amplifier A, and shifting the output DC level downward as shown in Figure 6(C). can do.

The RF signal amplitude can be made constant by adjusting the variable resistor VR1. However, since the RF signal Vout extracted by this RF signal amplification circuit can be expressed as the resistance value of the variable resistor VRI as Ra, when the input signal is large, the resistance value of the variable resistor VR1 becomes Correspondingly, the level shift will be the smallest.

[Objective of the Invention 1 This invention was made in order to improve the above-mentioned problem, and it is possible to keep the amplitude level constant without saturating the RF signal output due to variations in the optical pickup even if the drive voltage is lowered. An object of the present invention is to provide an optical disc playback device that can control the speed of playback.

[Summary of the invention] That is, the optical disc playback device according to the present invention has the following features:
A monitor element that detects the output level of the laser element, a first comparator circuit that compares the output of the monitor element and a first reference voltage and extracts the difference voltage, and generates a pulse signal of a predetermined period and detects the pulse signal. a first pulse width modulation means for modulating the pulse width according to the differential voltage, and a switching element whose switching is controlled by the output pulse of the first pulse width modulation means, and a pulse obtained through the switching element. a laser element drive circuit that rectifies and smoothes a voltage and supplies it as a drive voltage to the laser element; a peak detection circuit that detects the peak level of the output of the optical pickup; and a peak detection circuit that detects the output of the peak detection circuit and a second reference voltage. a second comparator circuit that compares and extracts the difference voltage;
a second pulse width modulation means for variably controlling the output pulse width of the first pulse width modulation means according to the output of the comparison circuit; The invention is characterized by comprising a means for operating only when the output level of the controller is equal to or higher than a predetermined level.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG.

Figure 1 shows how the focus error signal FE, tracking error signal TE, and laser output error output are controlled by pulse width variation DI (PWM) t in order to reduce the power consumption of the focus servo circuit, tracking servo circuit, and laser output control circuit.
,,PW each actuator and laser diode LD
This figure shows a configuration in which the present invention is applied to a 3-beam type CD playback device driven by M-BTL (balanced transformerless). A four-part main detector 22 and 23 receives and photoelectrically converts the disk reflected light of the main beam, and 22 and 23 are sub-subs that receive and photoelectrically convert the reflected light of two sub-beams irradiated on both sides of the bit string. A and C, and B and D of the outputs of each light receiving area A=D of the four-divided main detector 21 are added with current, respectively, and then the first and second
It is converted into a voltage signal by the IV conversion circuits 241 and 242. These two voltage signals are sent to the first subtraction circuit 25.
1, the well-known focus error signal FE
At the same time, the voltages are added by the level shift adder circuit 26 and supplied as an RF signal to a data slice circuit (EFM demodulation circuit), not shown.

On the other hand, the outputs of the light receiving areas E and F of the two sub-detectors 22 and 23 are subtracted by third and fourth t-V conversion circuits 243 and 244, respectively, and are taken out as a well-known tracking error signal TE.

In addition, 27 in the figure is a laser output control circuit, and this laser output control circuit 21 includes a monitor diode MO and a variable resistor VR.
2, a monitor voltage detection circuit 271 consisting of a resistor R4, a current source 11, 12, an error voltage detection circuit 212 consisting of a resistor R5 and an operational amplifier A2, a current source 13. Integrating capacitor C1, switch S1 whose switching is controlled by carrier signal SC, reference voltage source E1, and comparator C
Pulse width modulation (PWM) signal generation circuit 2 consisting of MP1
γ3, resistors R6 to R8, switching transistor Q
1. Smoothing capacitor C2, diode D1, coil L
1. The LD drive circuit 274 includes smoothing capacitors C3 and C4 and a laser diode LD.

That is, this laser output control circuit 27 monitors the laser output of the laser diode LD with the monitor diode MD, and calculates the difference voltage ( error voltage).

Then, the current amount of the current source I3 is variably controlled according to this error voltage, and the charging speed of the capacitor C1 is changed. Here, since the capacitor C1 is discharged according to the trigger period of the carrier signal SO, the sawtooth wave voltage signal V ramp is supplied to the inverting input terminal (-) of the comparator CMP1. Therefore, the comparator CMPI compares the sawtooth voltage signal V ramp with the output 1 of the reference voltage source E1 supplied to the non-inverting input terminal (+) and outputs a pulse signal. Therefore, when the charging speed of the capacitor C1 is changed by changing the output of the current source I3,
The comparator CMP1 performs pulse width modulation (PWM) on the pulse output according to the output of the error voltage detection circuit 212. This PWM signal controls switching of the switching transistor Q1 of the LD drive circuit 274. L.D.
The drive circuit 274 rectifies and smoothes the switching output of the transistor Q1, supplies it to the laser diode LD, and drives it.

Thereby, the laser output of the laser diode LD is controlled so that the output VMD of the monitor diode M[) and the reference voltage V1 are always equal. In addition, in order to stop driving the laser diode LD, the carrier signal @Sc
It is only necessary to set the switch S1 to the H (high) level and turn on the switch S1.

In the CD reproducing apparatus, the RF multiplied signal is first supplied to the peak detection circuit 28, and peak detection is performed according to a time constant set by the detection capacitor C5 and the discharge resistor R9. The time constant is set to be sufficiently longer than the time constant of dropout caused by scratches in order to prevent the laser output from increasing abnormally due to scratches on the disk. Then, the output Vp of this peak detection circuit 28 is converted into a comparison circuit 29.
The differential voltage V29 is supplied to the operational amplifier A3 and compared with the output 2 of the reference voltage 'rAE2, and the difference voltage V29 is taken out and supplied to the control input terminal of the current source I2 to variably control the amount of current. . “That is, in the error voltage detection circuit 272, the reference voltage (O) is generated by the combined current 71-12 of the current sources (1 and I2) and the resistor R5, and is VO-(11-12
)R5. As described above, the current source I2 is an auxiliary current source controlled by the output V29 of the comparison circuit 29 that compares the RF multiplied signal peak value Vp output from the peak detection circuit 28 with the RF signal reference voltage 2. current +1
By controlling the output of the error voltage detection circuit 212, the reference voltage ■O of the error voltage detection circuit 212 is controlled by the RF multiplied signal peak value ■p.

Here, the RF multiplied signal peak value VrJlfiRF signal base!
l! If the voltage is higher than V2, the output V2 of the comparator circuit 29
9 controls to increase the output of the current +1i112. As a result, the reference voltage vO of the error voltage detection circuit 272
decreases and VMD>VO, so the output of the current source I3 of the PWM signal generation circuit 273 becomes smaller due to the difference voltage. Therefore, the slope of the sawtooth voltage signal V ramp supplied to the comparator CMP1 becomes smaller, the L level pulse width of the comparator output becomes narrower, and the on period of the switching transistor Q1 of the LD drive circuit 274 becomes shorter. Therefore, the laser output of the laser diode LD decreases, and the RF multiplied signal amplitude (peak value) decreases. In this way, in addition to normal laser output control, the laser output of the laser diode LD is automatically controlled so that the RF multiplied signal peak value Vp and the RF signal reference voltage V2 are equal.

Therefore, even when the drive voltage is lowered, the CD playback device described above cannot suppress the laser output and control its amplitude level to a constant level before the RF multiplied signal output is saturated due to variations in the optical pickup. can.

Note that if the focus servo is not activated in the focus search state, the I
The value becomes 2-0, and the laser output becomes maximum. If this becomes a problem that shortens the life of the laser diode, use the focus servo on signal (FOK signal) that detects that it is within the control range of the focus servo to
The reference voltage generation section of the error detection circuit 272 may be configured as shown in FIGS. (a) to (d). That is, in Figure (a), a series circuit of a current source 14 and a switch S2 that is turned off when the FOK signal is at H level is connected in parallel to a resistor R5, and when the focus is not on, VO = R5 ( [1-12-14) = R5 ([1-I4) (12=O), and when the focus is on, VO = R5 (It - I2
) becomes. (b) The diagram shows resistors RIO and F for resistor R5.
A series circuit of switch S3 that turns off when the OK signal is at H level is connected in parallel, and when the focus is not on, VO=R5/R10・(11-I2) =R5/R10・(II) ( 12=O),
When the focus is on, VO=R5(11-I2
) becomes. (C) The figure shows a series circuit in which the current source 11 is connected in parallel with the current source I5 and the switch S4 that is turned on when the FOK signal is at H level.When the focus is not on, VO=R5(1112 ) =R5・N (12=O), and when the focus is on, VO=R5(1
1+15-12). In other words, when any of the circuits shown in FIGS. (a) to (C) is out of focus, the reference voltage VO can be lowered to prevent the laser output from becoming too large. In addition, without using the FOK signal, the same figure (d)
As shown in the figure, the output ■p of the peak detection circuit 28 may be used for control. In other words, in the diagram (d), the current source I4 and the switching control signal Vc are high with respect to the resistor R5.
The output Vp of the peak detection circuit 28 and the reference voltage source E are connected in parallel to each other by connecting the series circuit of the switch S2 which turns off at the level
Comparator CMP2 compares the level with the output V3 of 3, and the output of this comparator CMP2 is used as the switching control signal SC.
The voltage is supplied to the control input terminal of the switch S2, and the switch S2 is turned off when the RF multiplied signal peak value Vp exceeds the reference voltage 3. In other words, when the RF multiplied signal is at a certain level or higher, it can be considered that the object is in focus.

Furthermore, the CD reproducing apparatus according to the present invention may be configured as shown in FIG. In other words, this CD playback device is R
Instead of detecting the F-fold signal peak value, each light receiving area E of the sub-detectors 22 and 23.

After converting the signal obtained at F into a voltage signal in the IV conversion circuits 243 and 244, the voltage is added in the level shift addition circuit 30 to generate a sub-beam addition signal 5BAD, and this sub-beam addition signal 5BAD is added to the above-mentioned signal. Detection circuit 28
The time constant of the peak detection circuit 28 is set to be sufficiently longer than the time constant of dropouts caused by scratches on the disk, etc.
The output level of the reference voltage source E2 of No. 9 is set as the reference level for the sub-beam addition signal 5BAD. In other words, since the sub-beam addition signal 5BAD is considered to be approximately proportional to the RF multiplied signal amplitude, the same effect can be obtained even by using its peak value. Furthermore, the present invention is not limited to the above-mentioned embodiments. For example, the laser output control circuit is not a PWM drive system, but a normal L-type drive system that directly controls the drive current of the laser diode LD according to the error voltage.
Similar effects can be obtained in the D output control circuit by controlling the drive current of the laser diode LD in accordance with the output V29 of the comparison circuit 29.

[Effects of the Invention] As detailed above, according to the present invention, even if the drive voltage is lowered, the RF
It is possible to provide an optical disc playback device that can control the amplitude level of the signal output to a constant level without saturating the signal output.

[Brief explanation of drawings]

FIG. 1 is a block circuit configuration diagram showing one embodiment of an optical disc playback device according to the present invention, FIGS. 2 and 3 are block circuit diagrams showing other embodiments of the invention, and FIG. 6 through 6 are a block circuit diagram and an RF signal output waveform diagram, respectively, for explaining the RF signal detection means of the optical disc reproducing apparatus. 21...4-split main detector, 22.23...
Sub-detector, 241-244... I-V conversion circuit, 251° 252... Subtraction circuit, 26... Level shift addition circuit, 27... Laser output control circuit, 271
...Monitor voltage detection circuit, 272...Error voltage detection circuit, 273...PWM signal generation circuit, 274...
LD drive circuit, 28...Peak detection circuit, 29...
Comparison circuit, MD...monitor diode, LD...laser diode, FE...focus error signal, T
E...Tracking error signal, SC...Carrier signal. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] In an optical disc playback device that reads out the information signal by irradiating the optical disc on which the information signal is recorded with a laser beam emitted from a laser element using an optical pickup and receiving the reflected light, A monitor element that detects the output level of the laser element, a first comparator circuit that compares the output of the monitor element and a first reference voltage and extracts the difference voltage, and generates a pulse signal of a predetermined period and detects the pulse signal. a first pulse width modulation means for modulating the pulse width according to the differential voltage, and a switching element whose switching is controlled by the output pulse of the first pulse width modulation means, and a pulse obtained through the switching element. a laser element drive circuit that rectifies and smoothes a voltage and supplies it to the laser element as a drive voltage; a peak detection circuit that detects the peak level of the output of the optical pickup; and an output of the peak detection circuit and a second reference voltage. a second comparator circuit that compares the two and extracts the difference voltage;
a second pulse width modulation means for variably controlling the output pulse width of the first pulse width modulation means according to the output of the comparison circuit; 1. An optical disc reproducing apparatus, comprising means for operating the optical disc only when the output level of the optical disc is equal to or higher than a predetermined level.